Django specify which database to use for module - django

Question

In my Django project I have a couple of applications, one of them is email_lists and this application does a lot of data handling reading data from the Model Customers. In my production environment I have two databases: default and read-replica. I would like all queries in a particular module to be made against the replica-set database.
I can do that if I explicitly tell the query to do so:
def get_customers(self):
if settings.ENV == 'production':
customers = Customer.objects.using('read-replica').filter()
else:
customers = Customer.objects.filter()
but this module has more than 100 queries to the Customer and other models. I also have queries to relations like:
def get_value(self, customer):
target_sessions = customer.sessions.filter(status='open')
carts = Cart.objects.filter(session__in=target_sessions)
the idea is that I want to avoid writing:
if settings.ENV == 'production':
instance = Model.objects.using('read-replica').filter()
else:
instance = Model.objects.filter()
for every query. There are other places in my project that do need to read from default database so it can't be a global setting. I just need this module or file to read using the replica.
Is this possible in Django, are there any shortcuts ?
Thanks

Answer 1

You can read on django database routers for this, some good examples can be found online as well and they should be straightforward.
--
Another solution would be to modify the Model manager.
from django.db import models
class ReplicaRoutingManager(models.Manager):
def get_queryset(self):
queryset = super().get_queryset(self)
if settings.ENV == 'production':
return queryset.using('read-replica')
return queryset
class Customer(models.Model):
...
objects = models.Manager()
replica_objects = ReplicaRoutingManager()
with this, you can just use the normal Customer.objects.filter and the manager should do the routing.
I still suggest going with the database router solution, and creating a custom logic in the class. But if the manager works for you, its fine.

Answer 2

If you want All the queries in the email_lists app to query read-replica, then a router is the way to go. If you need to query different databases within the same app, then #ibaguio's solution is the way to go. Here's a basic router example similar to what I'm using:
project/database_routers.py
MAP = {'some_app': 'default',
'some_other_app': 'default',
'email_lists': 'read-replica',}
class DatabaseRouter:
def db_for_read(self, model, **hints):
return MAP.get(model._meta.app_label, None)
def db_for_write(self, model, **hints):
return MAP.get(model._meta.app_label, None)
def allow_relation(self, object_1, object_2, **hints):
database_object_1 = MAP.get(object_1._meta.app_label)
database_object_2 = MAP.get(object_2._meta.app_label)
return database_object_1 == database_object_2
def allow_migrate(self, db, app_label, model=None, **hints):
return MAP.get(app_label, None)
In settings.py:
DATABASE_ROUTERS = ['project.database_router.DatabaseRouter',]
It looks like you only want it in production, so I would think you could add it conditionally:
if ENV == 'production':
DATABASE_ROUTERS = ['project.database_router.DatabaseRouter',]